Systems and Methods for Heat Recovery Steam Generation at Dual Pressures

ABSTRACT

Systems for the recovery of heat from hot air exhaust from industrial processes, and the utilization of recovered heat to generate steam at two discrete (high and low) pressures. The systems match steam production with demand. The systems utilize efficient finned tube exchange units made up of modular sections that can be selectively associated with either high or low pressure steam generators. The systems utilize separate steam domes for each of the discrete steam pressures. The steam dome components may be structured apart from the heat exchange components. Each steam dome utilizes its own sensor and control instrumentation to vary the allocation of heat recovered to either or both the high or low pressure steam generator. The two generator subsystems are linked to operate variably according to demand. Monitoring upstream heat and downstream steam requirements allow for automated operation and allocation of recovered heat into the two subsystems.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims the benefit under Title 35 United States Code§119(e) of U.S. Provisional Application 61/613,403 filed Mar. 20, 2012,the full disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to systems for the recovery ofheat from industrial processes and the generation of steam there from.The present invention relates more specifically to a system forrecovering heat from an industrial process and generating steam at bothhigh and low pressures with the recovered heat.

2. Description of the Related Art

Many industrial processes utilize both high pressure and low pressuresteam to carry out the manufacturing or industrial process. Suchindustrial processes generally also generate and release heat into theatmosphere as part of the operation of the industrial system. It isoften desirable to recapture energy in the form of heat from such hotair streams that might otherwise be lost into the atmosphere. Thepresent invention not only captures such otherwise lost energy fromindustrial hot air streams, but also generates steam that can beutilized within the industrial processes in a manner that recycles aportion of the energy and reduces the need for ancillary energy tooperate the process. As part of this efficiency, the present inventionis structured to permit the generation of steam from the recovered heatat both high pressure and low pressure, thereby providing dual pressuresteam back to the industrial process rather than a single pressure steamflow.

One objective of the present invention is to produce both high pressureand low pressure steam from the same unit. The advantage of such adevice over systems previously employed is that it makes it easier tomatch the steam production with the steam demand within the plant ormanufacturing facility. If only high pressure steam is generated from aheat recovery system, then there would still be a considerable amount ofheat left in the hot air stream that would continue to be lost to theatmosphere. This is because the exit air temperature of the hot airstream can not be lower than the temperature of the steam beingproduced. On the other hand, if only low pressure steam is generated, itis often the case that too much steam is generated for the demand and aconsiderable amount of energy must again be released into theatmosphere.

SUMMARY OF THE INVENTION

The present invention provides systems and methods for the recovery ofheat from hot air exhaust streams produced by a wide variety ofindustrial processes, and the utilization of that recovered heat togenerate steam at two discrete (high and low) pressures. By adjustingand balancing the use of the recovered heat to produce more or less highpressure steam and low pressure steam, the system of the presentinvention is able to match steam production with the demand for steamwithin the plant or manufacturing facility. The system utilizes a highlyefficient finned tube exchange unit made up of multiple modular sectionsthat can be selectively associated with either the high pressure steamgenerator or the low pressure steam generator. In conjunction with thearray of modular exchange sections, the present invention utilizes aseparate steam dome for each of the discrete steam pressures generated.The steam dome (two in the preferred embodiment) components may bestructured and supported apart from the heat exchange components inorder to reduce the overall weight of the basic unit. Each steam domeutilizes its own instrumentation and ancillary flow equipment (levelcontrols, pressure switches, safety valves, etc.) in order to vary theallocation of heat recovered to either or both of the high pressuresteam generator or the low pressure steam generator. The two discretesteam generator systems are linked so as to be capable of operatingvariably according to demand. To facilitate this, the modular heatexchanger sections each have their own inlet and outlet tubings builtinto the frame of each section. These heat exchanger sections may thenbe selectively directed to either the high pressure steam dome or thelow pressure steam dome. Monitoring of the upstream heat being releasedand the downstream steam requirements allow for manual or automatedoperation and allocation of the recovered heat into the two sub-systemswithin the steam generator unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A & 1B are schematic flow diagrams of the overall system of thepresent invention divided across two pages for clarity.

FIG. 2 is a perspective view of a first preferred embodiment of thepresent invention showing the heat exchange components and the dualsteam dome components.

FIG. 3 is a front elevational view of the first preferred embodiment ofthe present invention shown and described above in conjunction with FIG.2.

FIG. 4 is a top plan view of the first preferred embodiment of thepresent invention shown and described above in connection with FIG. 2.

FIG. 5 is a side elevational view of the first preferred embodiment ofthe present invention shown and described above in connection with FIG.2.

FIG. 6 is a schematic block diagram showing the typical quantitativefunctioning of the system of the present invention, providingrepresentative quantities of high pressure and low pressure steamgenerated with a given hot air flowthrough.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is made first to FIGS. 1A & 1B which show in a schematic flowdiagram the overall system of the present invention divided across twopages for clarity. FIGS. 1A & 1B disclose not only the liquid and gasflow lines, but also the hot air exhaust flow through the system. Inaddition, an array of sensors and electronic control devices are shownincorporated into the system for carrying out the automated operation ofthe system based upon levels, temperatures, and pressures within thesystem. An actual unit constructed according to the system and methoddescribed herein may appear as in the structural configuration shown inFIGS. 2-5. The schematic diagram of FIGS. 1A & 1B represents just such astructural system, albeit omitting certain ancillary components thatwould be optional and apparent to those skilled in the art of steamgenerators and heat exchange systems. The fundamental features of thepresent invention are disclosed and described in detail in the schematicof FIGS. 1A & 1B.

FIG. 1A discloses most of the external flow lines that connect into orout from the system of the present invention, as well as one-half of theheat exchange component of the system (the half associated with the lowpressure steam generator side of the system). FIG. 1B represents thehigh pressure steam side of the heat recovery steam generating (HRSG)system associated with the first half of the heat exchange component. Asindicated above, various electrical and electronic signal connectionsare made throughout the system to various sensors in the form ofpressure gauges, level sensors, temperature sensors, and flow meters.Additionally, a number of remotely operated (electronic signal line)valves, pumps, and pressure release devices are shown to be operable inconjunction with automated control systems for such steam generatorenvironments within plants and manufacturing facilities.

Reference is next made to FIG. 2 for a structural view of an example ofa first preferred embodiment of the present invention shown implementedin conjunction with a heat exchange steam generator system of modestscale and complexity. In FIG. 2, heat recovery steam generator (HRSG)system 10 is made up primarily of heat exchange unit 12 and two steamdome/steam generator components 14 & 16. In the view shown in FIG. 2,steam dome 14 provides the high pressure steam generation, while steamdome 16 provides the low pressure steam generation. Hot exhaust airflows through heat exchange unit 12 through a bank of finned tubeexchange sections that make up a single heat exchange unit 12. Thenumber of heat exchange sections 20 that make up unit 12 may increase ordecrease depending upon the demands of the system and the industrialprocess that the unit is associated with Flow from the steam domes intothe heat exchange unit is carried out through the array of flow lines 26(30 for high pressure steam dome) and the return from the heat exchangeunit to the steam domes is carried out by way of return lines 24 (14 forhigh pressure steam dome) and return lines 22 (16 for low pressure steamdome). Each steam generator sub-system, made up primarily of steam domes14 & 16, carries its own operational control and instrumentationassembly 28, typically comprising the necessary control valves, levelsensors, pressure sensors, and other elements required for monitoringand controlling the operation of the overall system.

Reference is next made to FIG. 3 which is a front elevational view ofthe system shown generally in FIG. 2. In this view, system 10 again isshown to comprise heat exchange unit 12 as well as high pressure steamdome 14 and low pressure steam dome 16. In this view, the flow of hotexhaust air through the system occurs from the right hand side at airflow 36 and exits to the left hand side of this view at air flow 38.Operational monitoring and control once again occurs at control assembly28 for high pressure steam generator sub-system and at control assembly32 for low pressure steam generator sub-system. Flow lines 26 from highpressure steam dome 14 are shown directed into heat exchange sections 34as described above. In a similar manner, low pressure steam dome 16 isconnected by flow lines 30 to heat exchange sections 20 on the left handside of the system. In this manner, the hottest exhaust air enters thesystem on the high pressure steam generator side and exits the system onthe low pressure steam generator side.

FIG. 4 discloses in additional detail a top plan view of the overallsystem 10 described above, again showing the manner in which the exhaustgas flows through the system.

FIG. 5 shows an elevational view of the side of the system, describingin greater detail the array of sensor and control components associatedwith each of the steam dome/steam generator sub-systems.

Reference is finally made to FIG. 6 which provides a schematic blockdiagram showing the typical quantitative functioning of the system ofthe present invention. This schematic presents the production ofrepresentative quantities of high pressure and low pressure steam. FIG.6 provides as an example, the operation of the system of the presentinvention at an altitude of 200 m (for atmospheric pressure purposes)with a total energy recovered at 3153 kW. In this example, exhaust airinlet temperature is a representative 360° C. with a flow of 1400 cubicmeters per minute. Various density and humidity parameters to theexhaust flow are likewise provided in the figure. A heat transfertotaling 1804 kW occurs in the high pressure heat recovery steamgeneration stage of the process. This generates steam at a pressure of17 barg at a temperature of 207° C. Source condensate is provided to thehigh pressure side of the system at 0.3 barg and a condensatetemperature of 107° C. The exhaust air temperature after the highpressure steam stage of the system is a typical 235° C.

The low pressure steam generation stage of the system accomplishes aheat transfer of 1350 kW and produces steam at a pressure of 1 barg anda temperature of 120° C. The exhaust air outlet from the low pressureHRSG may be a typical 140° C. Source condensate is again provided to thelow pressure HRSG at pressure 0.3 barg and a condensate temperature of107° C.

Consideration of the heat recovered as shown in FIG. 6 indicates thatthe system provides a highly efficient mechanism for recovering energyotherwise lost from an industrial process and recycling it into theproduction of both high pressure and low pressure steam. The ability tobalance and allocate the steam production in this manner between thedual pressures allows for a greater amount of energy to be recovered andre-utilized in the industrial process.

Although the present invention has been described in conjunction with anumber of preferred embodiments, those skilled in the art will recognizemodifications to these embodiments that still fall within the scope ofthe invention. Variations in the temperature and flow rate of theexhaust air inlet into the system may require corresponding variationsin both the size and geometry of the heat exchange sections that make upthe heat exchange unit. The modular construction of the heat exchangeunit in the present invention lends itself to easy modification of thesize and of the allocation of the heat exchange sections to the overallsystem and to the separate high pressure steam and the low pressuresteam generating stages of the system. Various levels of automatedoperation of the system are also anticipated. A given industrial processthat does not itself vary in its heat output may require littlemodification of an established balance between the generation of highpressure steam and low pressure steam.

Other industrial processes may require an ongoing monitoring and balanceof the system based upon exhaust air temperatures and flows, as well asprocess steam requirements (high pressure or low pressure). The systemof the present invention provides a versatile and easily modifiablesystem for recovering heat from an exhaust air flow in an industrialprocess and directing and utilizing that heat to efficiently generatesteam in a balanced allocation of high pressure steam and low pressuresteam.

I claim:
 1. A steam generation system for recovering heat fromindustrial process hot air exhaust streams and generating steam at twodiscrete pressures, the system thereby defining a high pressure steamgeneration subsystem and a low pressure steam generation subsystem, theoverall steam generation system comprising: a finned tube heat exchangeunit positioned in association with the hot air exhaust streams, theheat exchange unit comprising a plurality of modular sections, theplurality of modular sections selectively associated with either thehigh pressure steam generation subsystem or the low pressure steamgeneration subsystem; and first and second steam domes operable inconjunction with the plurality of modular sections of the heat exchangeunit, the first and second steam domes discretely associated with thetwo steam generation subsystems, the steam domes structured andsupported apart from the heat exchange unit.
 2. The system of claim 1wherein each steam dome further comprises separate controlinstrumentation and ancillary flow equipment.
 3. The system of claim 2wherein the ancillary flow equipment comprises level controls, pressureswitches, and safety valves, the ancillary flow equipment provided tovary the allocation of heat recovered to the generation of either orboth high pressure steam or low pressure steam.
 4. The system of claim 1wherein the high and low pressure steam generation subsystems areoperationally linked to operate variably according to demand.
 5. Thesystem of claim 4 wherein each of the plurality of modular heatexchanger sections comprise discrete inlet and outlet connections,whereby the heat exchanger sections may be selectively directed toeither the high pressure steam dome or the low pressure steam dome. 6.The system of claim 1 further comprising an upstream heat monitor formeasuring a quantity of upstream heat being released and a downstreamsteam requirement monitor for measuring a quantity of high pressuresteam required and a quantity of low pressure steam required.
 7. Thesystem of claim 6 further comprising automated control instrumentationfor allocation of the recovered heat into the two subsystems within thesteam generator unit.